U.S. patent application number 10/529157 was filed with the patent office on 2006-11-30 for enzyme-sensitive therapeutic wound dressings.
Invention is credited to Derrek Slloock, Patrick Trotter.
Application Number | 20060269590 10/529157 |
Document ID | / |
Family ID | 9945076 |
Filed Date | 2006-11-30 |
United States Patent
Application |
20060269590 |
Kind Code |
A1 |
Trotter; Patrick ; et
al. |
November 30, 2006 |
Enzyme-sensitive therapeutic wound dressings
Abstract
The invention provides a wound dressing comprising a therapeutic
agent and a matrix comprising polymers joined by cross-linkages
which cross-linkages comprise oligopeptidic sequences which are
cleavable by a protease associated with wound fluid such that the
rate of release of the therapeutic agent increases in the presence
of the protease.
Inventors: |
Trotter; Patrick; (Meanwood,
GB) ; Slloock; Derrek; (Skipton, GB) |
Correspondence
Address: |
PHILIP S. JOHNSON;JOHNSON & JOHNSON
ONE JOHNSON & JOHNSON PLAZA
NEW BRUNSWICK
NJ
08933-7003
US
|
Family ID: |
9945076 |
Appl. No.: |
10/529157 |
Filed: |
October 1, 2003 |
PCT Filed: |
October 1, 2003 |
PCT NO: |
PCT/GB03/04250 |
371 Date: |
October 13, 2005 |
Current U.S.
Class: |
424/445 ;
424/447; 514/1.3; 514/18.3; 514/2.3; 514/20.1; 514/9.4 |
Current CPC
Class: |
A61L 2300/602 20130101;
A61L 2300/404 20130101; A61L 2300/434 20130101; A61L 2300/402
20130101; A61L 15/32 20130101; A61L 2300/604 20130101; A61L 15/44
20130101 |
Class at
Publication: |
424/445 ;
424/447; 514/014; 514/015; 514/016; 514/017; 514/018 |
International
Class: |
A61K 38/10 20060101
A61K038/10; A61K 38/08 20060101 A61K038/08; A61K 38/06 20060101
A61K038/06; A61K 38/05 20060101 A61K038/05; A61L 15/16 20060101
A61L015/16 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 1, 2002 |
GB |
0222722.1 |
Claims
1. A wound dressing comprising a therapeutic agent and a matrix
comprising polymers joined by cross-linkages which cross-linkages
comprise, or consist of, oligopeptidic sequences which are
cleavable by a protease associated with wound fluid such that the
rate of release of the therapeutic agent increases in the presence
of the protease.
2. A wound dressing according to claim 1 wherein the protease is
associated with wound infection or ulcer formation.
3. A wound dressing according to claim 1 or 2 wherein the polymers
themselves are not degraded by the protease or other factors that
may be present in the wound environment.
4. A wound dressing according to claim 1, 2 or 3 wherein the
polymer is a synthetic polymer.
5. A wound dressing according to claim 4 wherein the polymer is a
polymer of N-(2-hydroxypropyl)methyacrylamide (HPMA).
6. A wound dressing according to any one of the preceding claims
wherein the oligopeptidic sequences consist of 3 to 15 amino
acids.
7. A wound dressing according to any one of the preceding claims
wherein the protease is elastase and wherein the oligopeptidic
sequence comprises or consists of lys-gly-ala-ala-ala-lys (SEQ ID
NO: 1) -Ala-Ala-Ala-, Ala-Ala-Pro-Val (SEQ ID NO: 2),
Ala-Ala-Pro-Leu (SEQ ID NO: 3), Ala-Ala-Pro-Phe (SEQ ID NO: 4),
Ala-Ala-Pro-Ala (SEQ ID NO: 5) or Ala-Tyr-Leu-Val (SEQ ID NO:
6).
8. A wound dressing according to any one of claims 1 to 6 wherein
the protease is a matrix metalloproteinase and wherein the
oligopeptidic sequence comprises or consists of
-Gly-Pro-Y-Gly-Pro-Z- (SEQ ID NO: 7), -Gly-Pro-Leu-Gly-Pro-Z- (SEQ
ID NO: 8), -Gly-Pro-Ile-Gly-Pro-Z- (SEQ ID NO: 9), or
-Ala-Pro-Gly-Leu-Z- (SEQ ID NO: 10), where Y and Z are amino
acids.
9. A wound dressing according to any one of claims 1 to 6 wherein
the protease is a collagenase and wherein the oligopeptidic
sequence comprises or consists of -Pro-Leu-Gly-Pro-D-Arg-Z- (SEQ ID
NO: 11), -ProLeu-Gly-Leu-Leu-Gly-Z- (SEQ ID NO: 12),
-Pro-Gln-Gly-Ile-Ala-Gly-Trp- (SEQ ID NO: 13), -Pro-Leu-Gly-Cys
(Me)-His- (SEQ ID NO: 14), -Pro-Leu-Gly-Leu-Trp-Ala- (SEQ ID NO:
15), -Pro-Leu-Ala-Leu-Trp-Ala-Arg- (SEQ ID NO: 16), or
-Pro-Leu-Ala-Tyr-Trp-Ala-Arg- (SEQ ID NO: 17), where Z is an amino
acid.
10. A wound dressing according to any one of claims 1 to 6 wherein
the protease is a gelatinase and wherein the oligopeptidic sequence
comprises or consists of -Pro-LeuGly-Met-Trp-Ser-Arg- (SEQ ID NO:
18).
11. A wound dressing according to any one of claims 1 to 6 wherein
the protease is thrombin and wherein the oligopeptidic sequence
comprises or consists of -Gly-Arg-Gly-Asp- (SEQ ID NO: 19),
-Gly-Gly-Arg-, -Gly-Arg-Gly-Asp-Asn-Pro- (SEQ ID NO: 20),
-Gly-Arg-Gly-Asp-Ser- (SEQ ID NO: 21),
-Gly-Arg-Gly-Asp-Ser-Pro-Lys- (SEQ ID NO: 22), -Gly-Pro-Arg-,
-Val-Pro-Arg-, or -Phe-Val-Arg-.
12. A wound dressing according to any one of claims 1 to 6 wherein
the protease is stromelysin and wherein the oligopeptidic sequence
comprises or consists of -Pro-TyrAla-Tyr-Trp-Met-Arg- (SEQ ID NO:
23).
13. A wound dressing according to any one of the preceding claims
wherein the therapeutic agent is an antimicrobial agent, a pain
relieving agent, an antiseptic, an analgesic, a local anaesthetic,
or a protease inhibitor.
14. A wound dressing according to any one of the preceding claims
wherein the therapeutic agent is incorporated within the
matrix.
15. A wound dressing according to claim 14 wherein the wound
contacting layer of the dressing may comprise or consist of the
matrix within which the therapeutic agent is incorporated.
16. A wound dressing according to claim 15 wherein the dressing
comprises a liquid permeable wound contacting layer, an
intermediate layer comprising or consisting of the matrix within
which the therapeutic agent is incorporated and an outer,
liquid-impervious backing layer.
17. A wound dressing according to any one of claims 1 to 13 wherein
the dressing comprises a barrier layer which comprises the matrix,
the barrier layer being for initially separating the therapeutic
agent in the wound dressing from wound fluid when in use.
18. A wound dressing according to claim 17 wherein the barrier
layer comprises an apertured sheet having a composition comprising
the cross-linked polymers applied thereto in occlusive fashion.
19. A wound dressing according to claim 17 or 18, wherein a layer
of the therapeutic substance is provided behind the barrier
layer.
20. A wound dressing according to claim 19, wherein an absorbent
layer is provided behind the barrier layer and the therapeutic
substance is dispersed in the absorbent layer.
21. A wound dressing according to claim 17, wherein the barrier
layer substantially encapsulates the therapeutic substance.
22. A wound dressing according to any one of the preceding claims
wherein the wound dressing comprises an absorbent layer and/or a
backing layer.
Description
[0001] The present invention relates to wound dressing materials,
and in particular to new materials for the controlled release of
therapeutic agents into wounds.
[0002] All publications, patents and patent applications cited
herein are incorporated in full by reference.
[0003] In mammals, injury triggers an organised complex cascade of
cellular and biochemical events that result in a healed wound.
Wound healing is a complex dynamic process that results in the
restoration of anatomic continuity and function; an ideally healed
wound is one that has returned to normal anatomic structure,
function and appearance.
[0004] Infection of wounds by bacteria delays the healing process,
since bacteria compete for nutrients and oxygen with macrophages
and fibroblasts, whose activities are essential for the healing of
the wound. Infection results when bacteria achieve dominance over
the systemic and local factors of host resistance. Infection is
therefore a manifestation of disturbed host/bacteria equilibrium in
favour of the invading bacteria. This elicits a systemic septic
response, and also inhibits the multiple processes involved in
wound healing. Lastly, infection can result in a prolonged
inflammatory phase and thus slow healing, or may cause further
necrosis of the wound. The granulation phase of the healing process
will begin only after the infection has subsided.
[0005] Chronically contaminated wounds all contain tissue bacterial
flora. These bacteria may be indigenous to the patient or might be
exogenous to the wound. Closure or eventual healing of the wound is
often based on a physician's ability to control the level of the
bacterial flora.
[0006] If clinicians could respond to wound infection as early as
possible the infection could be treated topically as opposed to
having to use antibiotics. This would also lead to less clinical
intervention/hospitalisation and would reduce the use of
antibiotics and other complications of infection.
[0007] Current methods used to identify bacterial infection rely
mainly on judgement of the odour and appearance of a wound. With
experience, it is possible to identify an infection in a wound by
certain chemical signs such as redness or pain. Some clinicians
take swabs that are then cultured in the laboratory to identify
specific organisms, but this technique takes time.
[0008] Pain is also associated with infected and chronic wounds.
Biochemically, pain is experienced when there is an increase of
kinins (bradykinin) in the area of the wound. Kinins are produced
by the proteolytic breakdown of kininogen, and the protease
responsible for this is kallikrein. Kallikrein also stimulates the
production of tissue plasminogen activator (t-PA).
[0009] It has now been discovered that wound fluid from wounds that
are apparently not clinically infected but which go on to become
infected within a few days have elevated levels of neutrophil
elastase activity and may also have high levels of other
inflammatory enzymes, such as macrophage proteases, other
neutrophil proteases, bacterial collagenase, plasmin,
hyaluronidase, kallikrein or t-PA.
[0010] Further, chronic wounds, such as venous ulcers, pressure
sores and diabetic ulcers have a disordered wound-healing
metabolism even in the absence of infection. In particular, wound
chronicity is associated with elevated levels of protease enzymes
in the wound that interfere with the normal processes of tissue
formation and destruction in the wound.
[0011] It is known to provide antimicrobial wound dressings. For
example, such dressings are known having a liquid permeable wound
contacting layer, an intermediate absorbent layer and an outer,
liquid-impervious backing layer, in which one or more of the layers
contains an antimicrobial agent. For example, EP-A-0599589
describes layered wound dressings having a wound contacting layer
of a macromolecular hydrocolloid, an absorbent layer, and a
continuous, microporous sheet intermediate the wound contacting
layer and the absorbent layer. The absorbent layer contains a low
molecular weight antimicrobial agent that can diffuse into the
wound.
[0012] WO-A-0238097 describes wound dressings comprising a
liquid-permeable top sheet having a wound facing surface and a back
surface, and a hydrogel layer on the wound-facing surface of the
top sheet. The top sheet is adapted to block or restrict passage of
liquid from the back surface to the wound-facing surface. The
hydrogel layer is an insoluble hydrogel adapted to maintain a moist
wound-healing environment at the wound surface. The hydrogel may
contain therapeutic agents, such as antimicrobial agents, for
sustained release into the wound.
[0013] Previous antimicrobial wound dressings suffer from the
drawback that the release of the antimicrobial agent is relatively
unresponsive to the degree of infection of the wound being treated.
This is undesirable because it can result in resistant
microorganisms, and also because all unnecessary medication can
interfere with the processes of wound healing.
[0014] A first aspect of the invention provides a wound dressing
comprising a therapeutic agent and a matrix comprising polymers
joined by cross-linkages which cross-linkages comprise, or consist
of, oligopeptidic sequences which are cleavable by a protease
associated with wound fluid such that the rate of release of the
therapeutic agent increases in the presence of the protease.
[0015] Preferably, the matrix consists of the cross-linked polymers
and optionally also the therapeutic agent.
[0016] Preferably, the protease is associated with a wound healing
disorder, e.g. Infection, or ulcer formation (wound chronicity). In
this way, the rate of release of the therapeutic agent may increase
if the wound is infected or is a chronic wound.
[0017] By an "increase" in the rate of release of the therapeutic
agent we include the situation where the rate of release of the
therapeutic agent increases by at least 1.5, 2-, 3-, 4-, 5-, 6-,
7-, 8-, 9-, 10- or 15-fold. Preferably, there is no release of the
therapeutic agent in the absence of the protease.
[0018] By "a protease associated with wound infection" we include
proteases that are elevated during infection and proteases that are
elevated in wounds that are apparently not clinically infected but
which go on to become infected within a few days. Similarly, by "a
protease associated with ulcer formation" we include proteases that
are elevated in chronic wounds.
[0019] The principle underlying the present invention is that the
cross-linked polymers would behave as both an enzyme sensor and as
an enzyme-dependent delivery system. In the absence of the target
protease the oligopeptidic sequences remain intact, keeping the
pore size small and preventing (or at least keeping to low levels)
the release of the therapeutic agent. Elevated protease levels
(e.g. in wound infection or wound chronicity) hydrolyse the
oligopeptidic sequences which results in increased pore size and
permeability. The therapeutic agent is then released from the
dressing so that it is free to migrate into the wound. In this way,
delivery of the therapeutic agent increases in the presence of the
protease so that if the wound is infected (including as indicated
above when a protease associated with infection is elevated in a
wound that is apparently not clinically infected but which goes on
to become infected within a few days) or is a chronic wound
delivery of the therapeutic agent increases.
[0020] The term "polymer" as used herein includes homopolymers and
copolymers (e.g. random copolymers, alternating copolymers and
block copolymers).
[0021] Although polymers which are degraded by the target protease
could be used, it is preferred that the polymers are not degraded
by the target protease or other factors (e.g. other proteases) that
may be present in the wound environment.
[0022] In theory, any polymer containing groups to which the
reactive groups can be attached may be used, although of course the
skilled person will appreciate that considerations such as toxicity
should be taken into account. Similarly, the polymers used should
not be immunogenic.
[0023] In selecting a polymer, charge and size may also be
important as an increase in crystallinity will increase order and
therefore reduce permeability of barrier. The longer the polymers
the more likely they are to become physically intertwined, and
consequently the less likely they are to fall apart. In view of
this it is preferred that short polymers (i.e. 5 to 50 monomers)
are used.
[0024] Preferably, a polyfunctional polymer is used as the pore
size will be smaller and the ability to retain the therapeutic
agent in the absence of protease will be higher.
[0025] Preferably, the polymers are non-ionic surfactants,
polyalkoylated alcohols, alkyl or dialkyl polyglycerol compounds,
polyethyloxylated alcohols, polymers (including homopolymers and
copolymers) of acrylamide (e.g. N-(2-hydroxypropyl)methacrylamide
(HPMA)), polynucleotides, polypeptides or carbohydrates.
[0026] Preferably, the polymers are synthetic polymers. Examples of
synthetic polymers include polyvinyl alcohol, polyethylene
glycerol, PVP, polyolefins, fluoropolymers, hydropolymers from
vinyl esters, vinyl ethers, carboxy vinyl monomers, meth(acrylic)
acid, acrylamide, N-vinyl pyrrolidone, acylamidopropanem
acylamidopropane, PLURONIC (Maleic acid, NN-dimethylacrylamide
diacetone acrylamide acryloyl, morpholine and mixtures thereof, and
oxidized regenerated cellulose.
[0027] Alternatively, natural polymers such as carbohydrates (e.g.
dextan, chitin or chitosan) natural peptides or proteins
(collagens, elastin, fibronectins, or even soluble proteins such as
albumin), or semi synthetic peptides (made by using a peptide
synthesizer or by recombinant techniques) may be used.
[0028] In a preferred embodiment, polymers of
N-(2-hydroxypropyl)methyacrylamide (HPMA) are used. In this regard,
reference is made to Ulbrich et al. (1980) Biomaterials 1, 199-204,
which details the crosslinking of HPMA polymers by peptides.
[0029] As mentioned above, the polymers are joined by
cross-linkages which comprise cleavable oligopeptidic sequences.
Oligopeptides are generally defined as polypeptides of short
length, typically twenty amino acids or fewer. Preferably, the
oligopeptidic sequences employed in the present invention consist
of 3 to 15 amino acids, preferably 3 to 10 amino acids, more
preferably, 3 to 8 amino acids and yet more preferably 4 to 8 amino
acids. Preferably, the oligopeptidic sequences consist of 3, 4, 5,
6, 7 or 8 amino acids.
[0030] The degree of crosslinking of the polymers should be
sufficient such that the rate of release of the therapeutic agent
increases in the presence of the protease. Preferably, the degree
of crosslinking of the polymers should be sufficient to render the
matrix sufficiently impermeable to the molecule to be delivered so
that the therapeutic agent is only released in the presence of the
target protease. This will be dependent on the molecular weight of
the therapeutic agent.
[0031] The rate of degradation of the matrix will depend on a
number of factors, including the length of the oligopeptidic
sequences. Ulbrich et al. noted that extension of the peptidic
linkers by one amino acid residue to give a peptidic linker of four
amino acids caused a pronounced rise in the rate of cleavage of the
polymeric substrates. Ulbrich et al. reported that extension of the
oligopeptidic sequence led to a decrease in the steric hindrance by
polymer chain and thus to an increase in degradability.
[0032] Steric hindrance may also be reduced by coupling the
oligopeptidic sequence to the polymer by means of an appropriate
spacer. Thus, the oligopeptidic sequences may couple the polymers
directly (in which case the cross-linkage consists of the
oligopeptidic sequence) or by means of an appropriate spacer.
[0033] The following paper gives a useful review of bioconjugation
techniques for use in pharmaceutical chemistry: Veronese, F. M. and
Morpurgo, M (1999) Bioconjugation in Pharmaceutical chemistry II
Farmaco, 54, 497-516. This paper describes in detail the chemistry
of each amino acid and which ones are most suitable for use in
bioconjugation techniques. For example, it demonstrates that
conjugation would occur by nucleophile to electrophile attacks. The
amino acid side chains R--S--, R--NH2, R--COO-- and .dbd.R--O-- are
well suited to bioconjugation (to natural or synthetic
molecules).
[0034] In addition this paper indicates and gives examples of a
wide range of structures and chemical groups that the peptides
(containing amino (e.g. lysine), carboxyl (COO--) or cystyl groups
(R--SH) can bind to.
[0035] With regard to conjugation techniques, see also Ulbrich, K.,
et al (2000) Polymeric drugs based on conjugates of synthetic and
natural marcomolecules I. Synthesis and physico-chemical
characterisation. Journal of controlled release 64, 63-79. This
reference describes how antibodies, peptides or proteins can be
conjugated to synthetic polymers (e.g. poly HPMA).
[0036] The rate of degradation will not only depend on the number
of amino acids but also on the nature of the amino acids comprising
the cross-links. This dependency arises from the substrate specific
nature of proteases. The region of the enzyme where interaction
with the substrate takes place is known as the "active site" of the
enzyme. The active site performs the dual role of binding the
substrate while catalysing the reaction, for example cleavage.
Studies of the structures of the complexes of proteolytic enzymes
with peptides indicate that the active site of these enzymes is
relatively large and binds to several amino acid residues in the
peptide. Thus, the degradability of a particular bond in a peptide
chain depends not only on the nature of the structure near the
cleaved bond, but also on the nature of the amino acid residues
which are relatively remote from the cleaved bond, but play an
important part in holding the enzyme in position during
hydrolysis.
[0037] The structure of the oligopeptidic sequences must be chosen
so as to correspond to that of the active site of the protease
responsible for the degradation. The protease may be a host-derived
protease or a protease produced by pathogens (e.g. bacteria) at the
site of infection. Examples of such enzymes include, but are not
restricted to: matrix metalloproteinases and other extracellular
matrix component proteases (including collagenases, stromelysins,
matrilysin, gelatinases and elastases), lysosomal enzymes
(including cathepsin), serine proteases and other enzymes of the
clotting cascade (such as thrombin), enzymes of the endoplasmic
reticulum (such as cytochrome P450 enzymes, hydrolytic reaction
enzymes and conjugation reaction enzymes), non-specific
aminopeptidases and esterases, carboxypeptidases, phosphatases, and
glycolytic enzymes. Thrombin-like, alanine aminopeptidase, and
elastase-like enzymatic activity are common in bacterial
infections, and the amino acid cleavage sequences of such enzymes
are well-documented. WO 00/64486 discloses amino acid cleavage
sequences of various enzymes associated with wound infection.
[0038] Preferably, the protease is a macrophage or neutrophil
protease, or a human or bacterial collagenase or gelatinase. The
macrophage and neutrophil proteases include elastase, matrix
metalloproteinase 9 (MMP-9), MMP-8, cathepsin G, MMP-12, capases
and mixtures thereof.
[0039] Preferably, the protease is a collagenase, gelatinase,
elastase, matrix metalloproteinase, stromelysin, cathepsin G,
thrombin or capase.
[0040] In one embodiment, the protease is elastase and the
oligopeptidic sequence comprises or consists of
lys-gly-ala-ala-ala-lys, -Ala-Ala-Ala-, Ala-Ala-Pro-Val,
Ala-Ala-Pro-Leu, Ala-Ala-Pro-Phe, Ala-Ala-Pro-Ala or
Ala-Tyr-Leu-Val.
[0041] Preferably, the oligopeptidic sequence is cleavable by
elastase but is not cleavable by a MMP such as MMP-2 or MMP-9.
[0042] In another embodiment, the protease is a matrix
metalloproteinase and the oligopeptidic sequence comprises or
consists of -Gly-Pro-Y-Gly-Pro-Z-, -Gly-Pro-Leu-Gly-Pro-Z-,
-Gly-Pro-Ile-Gly-Pro-Z-, or -Ala-Pro-Gly-Leu-Z-, where Y and Z are
amino acids where Y and Z are amino acids.
[0043] In another embodiment, the protease is a collagenase and the
oligopeptidic sequence comprises or consists of
-Pro-Leu-Gly-Pro-D-Arg-Z-, -ProLeu-Gly-Leu-Leu-Gly-Z-,
-Pro-Gln-Gly-Ile-Ala-Gly-Trp-, -Pro-Leu-Gly-Cys(Me)-His-,
-Pro-Leu-Gly-Leu-Trp-Ala-, -Pro-Leu-Ala-Leu-Trp-Ala-Arg-, or
-Pro-Leu-Ala-Tyr-Trp-Ala-Arg-, where Z is an amino acid.
[0044] In another embodiment, the protease is a gelatinase and the
oligopeptidic sequence comprises or consists of
-Pro-LeuGly-Met-Trp-Ser-Arg-.
[0045] In another embodiment, the protease is a thrombin and the
oligopeptidic sequence comprises or consists of -Gly-Arg-Gly-Asp-,
-Gly-Gly-Arg-, -Gly-Arg-Gly-Asp-Asn-Pro-, -Gly-Arg-Gly-Asp-Ser-,
-Gly-Arg-Gly-Asp-Ser-Pro-Lys-, -Gly-Pro-Arg-, -Val-Pro-Arg-, or
-Phe-Val-Arg-.
[0046] In another embodiment, the protease is a stromelysin and the
oligopeptidic sequence comprises or consists of
-Pro-TyrAla-Tyr-Trp-Met-Arg-.
[0047] In one preferred embodiment of the invention, the protease
is elastase and the polymers are HPMA polymers and the
oligopeptidic sequences comprise or consist of
lys-gly-ala-ala-ala-lys, -Ala-Ala-Ala-, Ala-Ala-Pro-Val,
Ala-Ala-Pro-Leu, Ala-Ala-Pro-Phe, Ala-Ala-Pro-Ala or
Ala-Tyr-Leu-Val. Preferably, the oligopeptidic sequences directly
couple the HPMA polymers (i.e. without the presence of spacers). In
this example the terminal lysines may be added to bind the peptide
to the polymer.
[0048] Preferably, the oligopeptidic sequences are cleavable by
only one protease associated with wound fluid, preferably elastase.
Alternatively, the oligopeptidic sequences may be cleavable by two,
three or more proteases associated with wound fluid.
[0049] The design of the linking oligopeptidic sequence is
important as it must not only contain a hydrolysable sequence that
would be cleaved in the presence of the protease but also a
terminal amino acid that can be readily conjugated to the polymers
employed or to a spacer. Examples of reactive amino acids that
could be used to link the oligopeptidic sequences to the polymers
or spacers include cysteine and lysine.
[0050] The therapeutic agent may, for example, be an antimicrobial
agent and/or a pain relieving agent. The antimicrobial agent may,
for example, comprise an antiseptic, an antibiotic, or mixtures
thereof.
[0051] In selecting one or more therapeutic agents for use with the
wound dressings of the present invention, it is preferred that
larger molecules are employed (e.g. molecules having a molecular
weight of at least 500, 1,000, 5,000, 10,000, or 20,000). Small
molecules may penetrate the matrix, whereas larger molecules such
as chlorohexidine may be better suited to this type of application.
Bioerodible particles and colloidal silver are suitable. Although
it is preferred that the therapeutic agent is one which cannot
penetrate the matrix, it should nevertheless be appreciated that
small molecules such as silver salts may be employed since the
release of such therapeutic agents may still be to some extent
responsive to levels of protease as in the presence of elevated
levels of the target protease the cross-linkages which be cleaved
which will result in an increase in the rate of release of the
therapeutic agent. Further, if a polyfunctional polymer is used the
pore size of the matrix will be smaller and thus the ability of the
matrix to retain the therapeutic agent in the absence of protease
will be higher. Moreover, as noted above, the degree of
cross-linking will influence the permeability of the matrix.
[0052] Preferred antibiotics include peptide antimicrobials (e.g.
defensins, Magainin, synthetic derivatives of them) tetracycline,
penicillins, terramycins, erythromycin, bacitracin, neomycin,
polymycin B, mupirocin, clindamycin and mixtures thereof. Preferred
antiseptics include silver sulfadiazine, chlorhexidine, povidone
iodine, triclosan, other silver salts, sucralfate, quaternary
ammonium salts and mixtures hereof. The pain relieving agent may be
an analgesic or a local anaesthetic.
[0053] The therapeutic agent may be incorporated within the matrix
of the invention or may alternatively be located behind the matrix
in a "donor layer". Thus, in one embodiment of the first aspect
invention, the therapeutic agent is incorporated within the matrix.
For ready release of the therapeutic agent upon elevation of the
target protease, the therapeutic agent should not covalently bound
to the matrix. For example, if the molecule to be delivered is
relatively inert it could be mixed into the formulation during
manufacture. Silver is one example of a molecule that could be
delivered in this way. The wound contacting layer of the dressing
may comprise or consist of the matrix in which the therapeutic
agent has been incorporated into. Alternatively, the dressing may
comprise a liquid permeable wound contacting layer, an intermediate
layer (which may be an absorbent layer) comprising or consisting of
the matrix within which the therapeutic agent has been incorporated
and an outer, liquid-impervious backing layer. Upon degradation of
the matrix by proteases present in wound fluid, the therapeutic
agent present in the intermediate layer may diffuse into the
wound.
[0054] Another embodiment of the first aspect of the invention
provides a wound dressing which comprises a barrier layer which
comprises the cross-linked matrix of the invention, the barrier
layer being for initially separating the therapeutic agent in the
wound dressing from wound fluid when in use. Suitably, the barrier
layer consists of the matrix.
[0055] The barrier layer is separate from the therapeutic agent,
and the therapeutic agent is initially prevented from contacting
the wound fluid by the barrier layer. That is to say, the
bioavailability of the therapeutic agent to the wound surface is
low until the peptide cross-linkages in the barrier material have
been broken down by the enzyme, at which point the bioavailability
of the therapeutic agent increases. Since protease levels are
elevated in chronic and infected wounds, this provides for
accelerated and/or selective release of the therapeutic agent into
such wounds. The barrier layer is normally substantially impervious
to wound fluid and insoluble therein unless the wound fluid
contains a sufficient level of the specified enzyme to break down
the substrate material.
[0056] The barrier layer is preferably about 0.1 to about 3 mm
thick. Preferably about 0.5 to 1.5 mm thick. The cross-linked
polymers may be combined in a film-forming composition with
polymeric materials, plasticisers, and humectants. Suitable
polymers include alginates, guar gum, carboxymethyl cellulose,
methyl cellulose, hydroxypropyl methyl cellulose, locust bean gum,
carrageenan, chitosan, heparan sulfate, dermatan sulfate,
glycosaminoglycans such as hyaluronic acid, proteoglycans, and
mixtures thereof. Suitable plasticisers include C2-C8 polyhydric
alcohols such as glycerol. Preferably the cross-linked polymers
make up at least about 10% by weight, more preferably at least
about 20%, 30%, 40%, 50%, 60%, 70%, 80% or 90% by weight of the
film-forming composition.
[0057] In certain embodiments the barrier layer comprises a
substantially continuous film comprising the film forming
composition of the cross-linked polymers as described above.
[0058] In other embodiments the barrier layer comprises an
apertured sheet having a composition comprising the cross-linked
polymers applied thereto in occlusive fashion. The occlusive
composition may be similar to the film-forming composition
described above. In these embodiments, the apertures typically make
up from about 0.1% to about 50% of the area of the wound facing
surface of the sheet before swelling, more typically from about 1%
to about 30% of the area of the apertured sheet, and preferably
from about 10% to about 25% of the area of the apertured sheet.
Typically, the apertured sheet has from about 1 to about 30
apertures per square cm, for example from about 4 to about 15
apertures per square cm or from about 5 to about 10 apertures per
square cm. In certain embodiments the apertures are uniformly
distributed over the surface of the sheet, preferably in a regular
pattern. The mean area of each aperture may for example be from
about 0.01 to about 10 mm.sup.2, preferably from about 0.1 to about
4 mm.sup.2, and more preferably from about 1 mm.sup.2 to about 2
mm.sup.2. It will be appreciated that the sheet may include more
than one size and shape of aperture in order to provide apertures
that open more or less quickly on exposure to infected wound fluid.
This enables still more control over the dynamics of therapeutic
agent delivery to the wound. Typically, substantially the whole
area of the apertures in the apertured sheet is blocked by the
barrier material before exposure to wound exudate.
[0059] Preferably, the thickness of the barrier film or the
apertured sheet (by ASTM D374-79) is from about 0.2 to about 5 mm,
more preferably from about 0.4 to about 3 mm.
[0060] In one embodiment the barrier layer material may comprise,
in addition to the cross-linked matrix of the invention, a polymer
selected from the group consisting of water soluble macromolecular
materials (hydrogels) such as sodium alginate, sodium hyaluronate,
alginate derivatives such as the propylene glycol alginate
described in EP-A-0613692, and soluble hydropolymers formed from
vinyl alcohols, vinyl esters, vinyl ethers and carboxy vinyl
monomers, meth(acrylic) acid, acrylamide, N-vinyl pyrrolidone,
acylamidopropane sulphonic acid, PLURONIC (Registered Trade Mark)
(block polyethylene glycol, block polypropylene glycol)
polystyrene-, maleic acid, NN-dimethylacrylamide diacetone
acrylamide, acryloyl morpholine, and mixtures thereof. Suitable
hydrogels are also described in U.S. Pat. No. 5,352,508.
[0061] In one embodiment the barrier layer material may comprise,
in addition to the cross-linked matrix of the invention, a polymer
selected from the group consisting of bioerodible polymers such as
polylactide/polyglycolide, collagen, gelatin, polyacrylate gels
such as those described in EP-A-0676457, calcium alginate gels,
cross-linked hyaluronate gels, gels of alginate derivatives such as
propylene glycol alginate, and gels wherein the hydropolymer is
formed from vinyl alcohols, vinyl esters, vinyl ethers and carboxy
vinyl monomers, meth(acrylic) acid, acrylamide, N-vinyl
pyrrolidone, acylamidopropane sulphonic acid, PLURONIC (Registered
Trade Mark) (block polyethylene glycol, block polypropylene glycol)
polystyrene-, maleic acid, NN-dimethylacrylamide diacetone
acrylamide, acryloyl morpholine, and mixtures thereof. Suitable
hydrogels are also described in U.S. Pat. No. 5,352,508.
[0062] The barrier layer material may further comprise from about 5
to about 50% by weight, preferably from 15 to 40% by weight, on the
same basis of one or more humectants such as glycerol. The barrier
layer material may further contain up to about 30% w/w, more
preferably up to about 15% w/w on the same basis of water.
[0063] The matrix of the invention comprising the therapeutic agent
may contact the barrier layer directly, or may be separated
therefrom for example by an absorbent layer.
[0064] Preferably, the wound dressing of the invention comprises an
absorbent layer and/or a backing layer. As will be evident from the
above, the absorbent layer may, for example, separate the barrier
layer from the therapeutic agent containing cross-linked matrix or
alternatively the absorbent layer may comprise the therapeutic
agent containing cross-linked matrix.
[0065] The area of the optional absorbent layer is typically in the
range of from 1 cm.sup.2 to 200 cm.sup.2, more preferably from 4
cm.sup.2 to 100 cm.sup.2.
[0066] The optional absorbent layer may comprise any of the
materials conventionally used for absorbing wound fluids, serum or
blood in the wound healing art, including gauzes, nonwoven fabrics,
superabsorbents, hydrogels and mixtures thereof. Preferably, the
absorbent layer comprises a layer of absorbent foam, such as an
open celled hydrophilic polyurethane foam prepared in accordance
with EP-A-0541391, the entire content of which is expressly
incorporated herein by reference. In other embodiments, the
absorbent layer may be a nonwoven fibrous web, for example a carded
web of viscose staple fibers. The basis weight of the absorbent
layer may be in the range of 50-500 g/m.sup.2, such as 100-400
g/m.sup.2. The uncompressed thickness of the absorbent layer may be
in the range of from 0.5 mm to 10 mm, such as 1 mm to 4 mm. The
free (uncompressed) liquid absorbency measured for physiological
saline may be in the range of 5 to 30 g/g at 25.degree..
[0067] Preferably, the wound dressing further comprises a backing
layer covering the barrier sheet and the optional absorbent layer
on the side opposite the wound-facing side of the dressing. The
backing layer preferably provides a barrier to passage of
microorganisms through the dressing and further preferably blocks
the escape of wound fluid from the dressing. The backing layer may
extend beyond at least one edge of the barrier sheet (if present)
and optional absorbent layer to provide an adhesive-coated margin
adjacent to the said edge for adhering the dressing to a surface,
such as to the skin of a patient adjacent to the wound being
treated. An adhesive-coated margin may extend around all sides of
the barrier sheet (if present) and optional absorbent layer, so
that the dressing is a so-called island dressing. However, it is
not necessary for there to be any adhesive-coated margin.
[0068] Preferably, the backing layer is substantially
liquid-impermeable. The backing sheet is preferably semipermeable.
That is to say, the backing sheet is preferably permeable to water
vapour, but not permeable to liquid water or wound exudate.
Preferably, the backing sheet is also microorganism-impermeable.
Suitable continuous conformable backing sheets will preferably have
a moisture vapor transmission rate (MVTR) of the backing sheet
alone of 300 to 5000 g/m.sup.2/24 hrs, preferably 500 to 2000
g/m.sup.2/24 hrs at 37.5.degree. C. at 100% to 10% relative
humidity difference. The backing sheet thickness is preferably in
the range of 10 to 1000 micrometers, more preferably 100 to 500
micrometers.
[0069] Suitable polymers for forming the backing sheet include
polyurethanes and poly alkoxyalkyl acrylates and methacrylates such
as those disclosed in GB-A-1280631. Preferably, the backing sheet
comprises a continuous layer of a high density blocked polyurethane
foam that is predominantly closed-cell. A suitable backing sheet
material is the polyurethane film available under the Registered
Trade Mark ESTANE 5714F.
[0070] The adhesive layer (where present) should be moisture vapor
transmitting and/or patterned to allow passage of water vapor
therethrough. The adhesive layer is preferably a continuous
moisture vapor transmitting, pressure-sensitive adhesive layer of
the type conventionally used for island-type wound dressings, for
example, a pressure sensitive adhesive based on acrylate ester
copolymers, polyvinyl ethyl ether and polyurethane as described for
example in GB-A-1280631. The basis weight of the adhesive layer is
preferably 20 to 250 g/m.sup.2, and more preferably 50 to 150
g/m.sup.2. Polyurethane-based pressure sensitive adhesives are
preferred.
[0071] Preferably, the adhesive layer extends outwardly from the
absorbent layer and the envelope to form an adhesive-coated margin
on the backing sheet around the absorbent layer as in a
conventional island dressing.
[0072] Also within the scope of the present invention are
embodiments in which the cross-linked matrix material substantially
encapsulates the therapeutic agent. For example, the dressing may
comprise, or consist essentially of, particles such as microspheres
of therapeutic agent (e.g. antimicrobial material) encapsulated in
a layer comprising the cross-linked matrix material. The particles
are preferably loaded with from 1 to 90 wt. %, more preferably from
3 to 50 wt. % of the therapeutic agent.
[0073] The particles may be made by any suitable technique,
including comminution, coacervation, or two-phase systems for
example as described in U.S. Pat. No. 3,886,084. Techniques for the
preparation of medicated microspheres for drug delivery are
reviewed, for example, in Polymeric Nanoparticles and Microspheres,
Guiot and Couvreur eds., CRC Press (1986).
[0074] A preferred method for preparation of the microparticles is
coacervation, which is especially suited to the formation of
particles in the preferred size range of 100 to 500 micrometers
having a high loading of therapeutic agents. Coacervation is the
term applied to the ability of a number of aqueous-solutions of
colloids, to separate into two liquid layers, one rich in colloid
solute and the other poor in colloid solute. Factors which
influence this liquid-liquid phase separation are: (a) the colloid
concentration, (b) the solvent of the system, (c) the temperature,
(d) the addition of another polyelectrolyte, and (e) the addition
of a simple electrolyte to the solution. Coacervation can be of two
general types. The first is called "simple" or "salt" coacervation
where liquid phase separation occurs by the addition of a simple
electrolyte to a colloidal solution. The second is termed "complex"
coacervation where phase separation occurs by the addition of a
second colloidal species to a first colloidal solution, the
particles of the two dispersed colloids being oppositely charged.
Generally, materials capable of exhibiting an electric charge in
solution (i.e. materials which possess an ionizable group) are
coacervable. Such materials include natural and synthetic
macromolecular species such as gelatin, acacia, tragacanth,
styrene-maleic anhydride copolymers, methyl vinyl ether-maleic
anhydride copolymers, polymethacrylic acid, and the like.
[0075] If, prior to the initiation of coacervation, a
water-immiscible material, such as an oil, is dispersed as minute
droplets in an aqueous solution or sol or an encapsulating
colloidal material, and then, a simple electrolyte, such as sodium
sulfate, or another, oppositely charged colloidal species is added
to induce coacervation, the encapsulating colloidal material forms
around each oil droplet, thus investing each of said droplets in a
liquid coating of the coacervated colloid. The liquid coatings
which surround the oil droplets must thereafter be hardened by
cross-linking to produce solid-walled microcapsules
[0076] Preferably, the wound dressing according to any aspect of
the present invention is sterile and packaged in a
microorganism-impermeable container.
Sequence CWU 1
1
23 1 6 PRT Artificial Sequence Description of Artificial Sequence
Synthetic peptide 1 Lys Gly Ala Ala Ala Lys 1 5 2 4 PRT Artificial
Sequence Description of Artificial Sequence Synthetic peptide 2 Ala
Ala Pro Val 1 3 4 PRT Artificial Sequence Description of Artificial
Sequence Synthetic peptide 3 Ala Ala Pro Leu 1 4 4 PRT Artificial
Sequence Description of Artificial Sequence Synthetic peptide 4 Ala
Ala Pro Phe 1 5 4 PRT Artificial Sequence Description of Artificial
Sequence Synthetic peptide 5 Ala Ala Pro Ala 1 6 4 PRT Artificial
Sequence Description of Artificial Sequence Synthetic peptide 6 Ala
Tyr Leu Val 1 7 6 PRT Artificial Sequence Description of Artificial
Sequence Synthetic peptide 7 Gly Pro Xaa Gly Pro Xaa 1 5 8 6 PRT
Artificial Sequence Description of Artificial Sequence Synthetic
peptide 8 Gly Pro Leu Gly Pro Xaa 1 5 9 6 PRT Artificial Sequence
Description of Artificial Sequence Synthetic peptide 9 Gly Pro Ile
Gly Pro Xaa 1 5 10 5 PRT Artificial Sequence Description of
Artificial Sequence Synthetic peptide 10 Ala Pro Gly Leu Xaa 1 5 11
6 PRT Artificial Sequence Description of Artificial Sequence
Synthetic peptide 11 Pro Leu Gly Pro Arg Xaa 1 5 12 7 PRT
Artificial Sequence Description of Artificial Sequence Synthetic
peptide 12 Pro Leu Gly Leu Leu Gly Xaa 1 5 13 7 PRT Artificial
Sequence Description of Artificial Sequence Synthetic peptide 13
Pro Gln Gly Ile Ala Gly Trp 1 5 14 5 PRT Artificial Sequence
Description of Artificial Sequence Synthetic peptide 14 Pro Leu Gly
Cys His 1 5 15 6 PRT Artificial Sequence Description of Artificial
Sequence Synthetic peptide 15 Pro Leu Gly Leu Trp Ala 1 5 16 7 PRT
Artificial Sequence Description of Artificial Sequence Synthetic
peptide 16 Pro Leu Ala Leu Trp Ala Arg 1 5 17 7 PRT Artificial
Sequence Description of Artificial Sequence Synthetic peptide 17
Pro Leu Ala Tyr Trp Ala Arg 1 5 18 7 PRT Artificial Sequence
Description of Artificial Sequence Synthetic peptide 18 Pro Leu Gly
Met Trp Ser Arg 1 5 19 4 PRT Artificial Sequence Description of
Artificial Sequence Synthetic peptide 19 Gly Arg Gly Asp 1 20 6 PRT
Artificial Sequence Description of Artificial Sequence Synthetic
peptide 20 Gly Arg Gly Asp Asn Pro 1 5 21 5 PRT Artificial Sequence
Description of Artificial Sequence Synthetic peptide 21 Gly Arg Gly
Asp Ser 1 5 22 7 PRT Artificial Sequence Description of Artificial
Sequence Synthetic peptide 22 Gly Arg Gly Asp Ser Pro Lys 1 5 23 7
PRT Artificial Sequence Description of Artificial Sequence
Synthetic peptide 23 Pro Tyr Ala Tyr Trp Met Arg 1 5
* * * * *